The invention relates to the telecommunication field, and more particularly to a method and apparatus for managing contention in a self-routing switching architecture in a port expansion mode.
Patent applications 96480126.0 (FR996040), 96480125.2 (FR996041), 96480117.9 (FR996042), and 96480120.3 (FR996045) are non-published prior European patent applications representing examples of powerful self routing switches that provide high switching speed. However, it is generally highly desired to increase the number of ports that allow more access and attachments to the basic switch core. When the switch rate tends to increase, it is observed that the cell cycle concurrently decreases, while, conversely, the transit time tends to increase when the physical area of the switching architecture tends to increase. Particularly, it may well happen that the basic switching component of a switching architecture, the so-called switch fabric, is located in one physical area, while the Switch Core Access Layers (SCALs) that permit the attachments to the switch fabric are located in different physical locations. The communication between the SCALs and the switch fabric will be achieved by means of one or more serial communication links that may extend over several hundreds of meters.
Therefore, the two basic requirements, i.e., the decrease in the cell cycle and the increase in the physical length of the cables involved in the switching architecture, tend to create significant difficulties in the possibility of connecting individual switching structures in a port expansion mode, since the latter implies the design of an effective contention mechanism for providing the fan-in operations involved downward of the switch fabric. Obviously it could be possible to base the arbitration mechanism on a fixed bandwidth for every switching structure which appears to be not very effective. However, another approach requires that a specific fan-in mechanism be designed , which can compensate for the effects resulting from the difference in the delays and transfer time of the cells throughout the physical coaxial cables and optical links between the switch fabric and the SCALs.
The technical problem to be solved by the present invention is to permit a port expansion architecture that authorizes, on one hand, an increase in the switching rates (corresponding to decrease of the cell cycles), while, on the other hand, permitting a large physical area for the switch architecture where the different SCAL elements are distributed at a distance up to 500 meters from the switch cores.
This problem is solved by the method and apparatus for managing contention in a self-routing switching architecture based on a set of nxc3x97n individual switching structures that are connected in a port expansion mode by means of fan-out and fan-in circuits providing access of the Switch Core Access Layers (SCAL) to the different input and output ports of the switching core. The fan-in circuits use an arbitration mechanism for providing a token to the switch that is allowed to deliver the next cell and the arbiter operates based on detection of a special comma character in accordance with the 8B/10B coding which is introduced in the data flow between the individual switching structures and the fan-in circuits. This provides an automatic compensation for the difference in delays of transfer of the cells even when high switching speed and long length of the physical media are involved.